This invention relates generally to transferring voice and data over Internet systems and more particularly to an asymmetric Digital Simultaneous Voice/Data system that facilitates transmission of voice and data to different endpoints.
Many home users have only one phone line, and hence use Digital Simultaneous Voice/Data (DSVD) modems to simultaneously transfer voice and data at the same time over a common communication channel. DSVD modems conforming to a V.34 standard are beginning to become available at low cost and are expected to be ubiquitous in new consumer-oriented personal computers. PC hardware and software companies expect to significantly reduce support costs by providing concurrent voice and data access for help desks and support organizations.
Conventional DSVD operates as an “end-to-end” system. In an end-to-end system, a communication channel, such as through a Plain Old Telephone Service (POTS) telephone call, directly connects two endpoints at the physical channel level. End-to-end systems differ from “access” systems where the communication channel connects to a packet switched network such as the Internet.
FIG. 1 shows a typical implementation of DSVD as an end-to-end voice and data system 12. A telephone 14 and a personal computer 16 are each coupled to a conventional communication DSVD modem 18. The DSVD modem 18 is coupled through a Public Switched Telephone Network (PSTN) to a PBX telephone switching system 22. A second conventional DSVD modem 24 is coupled between the PBX 22 and a telephone 26 and a personal computer 28.
Referring to FIG. 2, each DSVD modem 18 and 24 includes a telephone interface 30 having a voice data port that connects to the telephone 14 (FIG. 1) for receiving analog voice signals. A UART 34 includes a data port that connects to the personal computer 16 (FIG. 1). The voice codec 32 is implemented either via a DSP or software running on a microprocessor, and digitizes the analog voice signal from telephone 14. The codec 32 then typically performs a voice compression algorithm based on a G.729 compression standard. A framer/multiplexer 36 is connected to both the codec 32 and the UART 34. The framer/multiplexer formats the voice and data into frames and then multiplexes the voice and data frames together into a continuous data stream. The data stream is transmitted by a V.34 data modem through a Data Access Arrangement (DAA) 40 over the PSTN 20.
The implementation of the DSVD modems 18 and 24 are symmetric meaning the voice data is encoded, compressed, and multiplexed with the computer character data for transmission at one end. The voice and character data is then de-multiplexed, decompressed, and decoded at the other end in a reverse manner. Such a scheme leads to a number of serious limitations on how DSVD may be employed.
In order to support both voice and data, symmetric DSVD requires a DSVD modem at both ends of the transmission channel. If one user has a DSVD modem and the other user only has a conventional modem used in conjunction with PC-based packet voice software, the two users cannot transmit voice data. Another substantial limitation is that DSVD systems are only capable of one physical channel switched connection at a time. Thus, in DSVD systems, the voice and data must always terminate at the same endpoint.
Consumers of the voice and data may not be at the same endpoint. For example, voice may be sent to a service representative for catalog company “A” while the data may be sent to a World Wide Web (WWW) site for company “B” to search for alternative pricing information. Other operations may also be performed on the transmitted voice stream, such as recording conversations, performing voice recognition, etc. However, the analog voice signal output from the DSVD modem cannot be directly processed in a digital signal processing environment. The analog voice signal would require reencoding back into a digital data format. Reencoding voice signals require additional time and signal processing circuitry. The quality of the voice signal also degrades each time the voice signal is encoded and decoded between an analog signal and digital data.
Accordingly, a need remains for a system that is more effective in transmitting and receiving voice and data to and from different network endpoints over the same communication channel.